Problem: $ { \left[\begin{array}{rrr}{2} & {-1} & {-1} \\ {-1} & {4} & {1}\end{array}\right]+\left[\begin{array}{rrr}{-1} & {0} & {-2} \\ {-1} & {-2} & {3}\end{array}\right] = {?} } $
To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rrr}{2}+{-1} & {-1}+{0} & {-1}+{-2} \\ {-1}+{-1} & {4}+{-2} & {1}+{3}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{1} & {-1} & {-3} \\ {-2} & {2} & {4}\end{array}\right]}$